Electric condenser



Oct. 25, 1932. P. c. RAWLS ELECTRIC CONDENSER Filed Feb. 24. 1950 Patented Oct. 25, 1932 UNITED STATES PATENT OFFICE YPAUL C. BAWLS, Ol' DES MOINES, IOWA, ASSIGNOR T0 TECHNICAL EQUIPMENT COI- PANY, OF DES IOINES, IOWAA CORPORATIONA OF IOITA.`

ELECTRIC CONDENSER Application led February 24, 1930. Serial No. 431,009.

The object of my invention is to provide an electric condenser especially adapted to be used in connection with radio circuits, of simple, durable and inexpensive construe tion, having a comparatively large capacity and .a compara-tively small external electrostatic eld, whereby the condenser when in operation will be comparatively free of external and foreign electro-static influence.

More specifically itr is the object of my invention to provide in an electric condenser of the type employing a rotatively mounted knob or dial for var lng the capacityof the condenser, improve construction whereby the electric capacit of the condenser will be varied more uni ormly during the entire angular movement of said knob between its maximum and minimum capacity positions, whereby a given angular movement of the operating knob at the beginning of the movement of the condenser late to increase its capacity will produce su stantially the same capacity of variation as it would at its opposite extreme position of movement.

A further ob]ect is to rovide a condenser of simple construction w ich may be `formed of stamped sheet metal, and wherebyV all of the condenser plates may be :formed by a single die. v

-My invention consists in the construction,

. arrangement and combination `of the various parts of the device, whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in my claim, and

'illustrated in the accompanying drawing, in

which:

Figure 1 is a side elevation of my improved condenser. f

Figure 2 is a detail sectional view taken on the line 2-2 of Figure 1.

' Figure 3 is a detail sectional view taken on the line 3-3 of Figure 2.

Figure 4; is a detail sectional view of a' slightly modified form of my improved condenser; and

Figure 5 is a perspective view of one of the condenser plates.

My improved condenser includes a series of sheet metal conductor plates, each of which is preferably formed of thin and resilient sheet metal, each of the plates having the form of a circular disc provided with a radially projecting terminal bar 11 and a second radially projecting anchor bar 12. The terminal'bar 11 is provided with an opening 13, and the bar 12 with an opening 14, the central part of the conductor plate being provided with an opening 15.

In its simplest form my condenser comprises a pair of said conductors 16 and 17, the plate 16 being secured to a suitable support 18 by means of a terminal bolt 19 and a rivet 20. A sheet of insulating material 21is then placed over the member 16 and held against rotation by stop rivets 22, the edge of the insulating block being notched to receive the rivet 20. The insulator 21 is provided with an opening 23 of smaller diameter than the opening 15 of the conductor 16. The conductor 17 is then placed in position on top of 1 the insulator 21 and secured in position by means of the terminal bolt 24 and an' anchor bolt 25, the conductor 17 being located opposite the conductor 16.

Before the conductor 17 is placed in posi tion the disc of the said conductor is bent in the form of a concavo-convex surface, the concave surface being placed adjacent to the insulator 21. An o erating bolt 26 is then projected through tllie openings 15 and both of the conductors 16 and '17 and through the opening 23 of the insulator 21 and through an opening 27 in the block 18, and finally screwthreaded into the stationary dial plate or block 28 having its outwardly projecting end provided with a knob 29 to which a pointer 30 1s secured in the manner clearly illustrated in Figures 1, 2 and 3.

By this construction it will be seen that a comparatively small amount of active area is present during the time that the concluetors 16 and 17 are in their open position, as illustrated in Figure 2.

1n this connection it should be borne in mind that the insulator r 21 is preferably formed of a comparatively thin sheet of mica, so that the engaging portions of the conductor 17 lie very close to the conductor 16, and the condenser will be provided with a compara' tively large capacity.

, trated in dotted lines in Figure 2, at .the same i time the active area of the plates being increased.

On account of the conductors 16 and 17 being of circular formation I iind that a compara-tively uniform capacity variation results with a given angular adjustment of the knob 29, this capacity variation being substantially the same either at the maximum opening of the condenser plates or at the .maximum closed position, so that a comparatively straight capacity curve would result when lotted with the angular adjustment of the nob 29. A

This is a very desirable feature, especially when the condenser is used in a tuning circuit to avoid critical tuning adjustment of the condenser on low frequency adjustments. I am well aware that the idea of moving two plates toward and from each other forV varying the capacity of the condenser, is not broadly new as used with an insulating material between the plates. I ind that if the condenser is com osed of two flat discs, one

of which is move toward and 'from the other and always in a parallel relation therewith, that the capacity of the condenser increases very slowly at the beginning of the closing movement, and4 very rapidly at the end of said closing movement, making the condenser ver critical in' tuning when in this position. ne advantage of my improved condenser lies in the fact that-both sets of plates or conductors are formed substantially identical with the exception that the plate 16'is provided with a larger opening than the con ductorv 17, so as to prevent electrical contact between the bolt 26 and the plate 16.

The anchor bars 12, together with the terminal bars 11, serve to rigidly hold the conductor plates against movement, the anchor bar 12 being preferably supported substantially 90 degrees from the terminal bar 11, so as to permit a slight amount of lateral movement of the free edge of the plate 17 as it is collapsed.

In Fi re 4 I have illustrated a slightly modifie form in which two oppositely arranged curved plates 32 and 33 having a central plate 34 are used, said plates being separated from the plates 32 and 33 by insulators This provides a condenser of twice the capacity of my preferred form, both sets of the termmal bars 11 of said plates 32 and 33 being secured to a common terminal bolt.

Thus. it will be seen that 1 have provided a simple, durable and inexpensive condenser which has a very uniform capacity curve, and which is very eiiicient in its operation masmuch as it is very compact and has a verv small external electro-static field compared with its internal capacity, and is very suitable for use with high frequency circuits.`

I claim as my invention:

An electric condenser comprising a base, a pair of similar circular conductors of substantially thexsame diameter concentrically arranged, an insulator between said plates, one of said plates being adjacent to said base and the other'bent to form a concavo-convex 

